I. Field of the Invention
The present invention relates to cellular telephone networks and, in particular, to a technique for facilitating the calling of emergency numbers from cellular telephones.
II. Description of the Related Art
In recent years, telephonic communication effectuated by way of a cellular, or other wireless, communication network has become increasingly popular. In such a system, signals are transmitted between two communication systems by way of radio frequency signals over radio frequency channels. Initiation of communication links in a cellular communication system is typically accomplished in a manner analogous to the initiation of telephonic communication links in a conventional wireline, telephonic system. A calling party initiates communication with a called party by entering an identification number, i.e., the telephone number, of the party to whom telephonic communication is to be effectuated. Network switching apparatus interprets the telephone number and provides the necessary connections to effectuate the telephonic communication.
In some sections of the United States, telephonic networks provide emergency "911" service. Other countries provide analogous service. In areas of the country which provide for "911" service, a caller requiring emergency assistance dials, or enters, the digits 9-1-1. When the telephonic network detects entry of such digits, connection of the calling party to a public safety answering point ("PSAP") is immediately effectuated. In other countries, other sequences of digits are entered by a caller, similarly to be connected to a PSAP or other emergency dispatch center.
Emergency or "911" calls originating from the cellular network are routed to a PSAP in a manner similar to that used for landline 911calls. However, due to the unique nature of the cellular system, other methods have also been established to aid in emergency call handling.
For example, it is known to have a 911 button, or some other pre-programmed button, on the terminal or mobile station. Unfortunately, such "pre-programmed" approaches present difficulties for those users who "roam" with their telephones (travel into service areas other than their home service area). Since some service areas use "911" as the emergency number and other areas use different numbers (e.g., "999"), a telephone pre-programmed with an emergency number corresponding to a particular service area may not be useful when the pre-programmed function is employed during emergency situations in other service areas. In addition, the provision of a dedicated emergency key entails a non-standard interface design, which may increase telephone complexity and expense.
Accordingly, a need in the art exists for a wireless telephone capable of facilitating the placement of emergency calls outside of a home service area.